66 IMS (On (CLELAWEDE/SILIONY. 
In the interior of the nebula the temperatures were probably 
far above the critical temperatures of all known substances, and 
this renders it improbable that central liquefaction prevailed 
during the nebular stages; indeed the very dispersion of the 
matter into so vast a volume as the Laplacian hypothesis postu- 
lates may perhaps be taken as an implicit assertion of the domi- 
nance of the gaseous laws throughout the mass. This is certainly’ 
the view of its ablest exponents. Lord Kelvin speaking of a 
globular gaseous nebula (selected to represent the primitive neb- 
ula), having the mass of the solar system and a radius forty 
times the radius of the earth’s orbit, says: ‘The density in its 
central regions, sensibly uniform throughout several million kilom- 
eters, is one twenty-thousand millionth of that of water; or 
one twenty-five millionth of that of air.”* Similar determinations 
may be found in the more elaborate computations of Darwin for 
varying dimensions of the nebula.* We are therefore apparently 
not dealing with densities, even in the central parts, greater than 
those covered by experimental evidence. 
Besides, the present distribution of matter in the solar system 
offers an independent argument against any great central lique- 
faction, until after the earth was separated at least, for, by hypoth- 
esis, the earth was formed from the extreme equatorial periphery 
of the nebula, but the larger part of its material is of the most 
refractory kinds known and would pass into the liquid and solid 
states early in the history of condensation. There seems little 
ground therefore for assuming any effective condensation of the 
central matter of the nebula during at least the early stages of 
planetary evolution. 
On the other hand, experimental evidence and theoretical 
deductions alike indicate that under very high pressures, where 
the temperature is also above the critical point, the density fails 
to increase as fast as the pressure. As these are the assigned 
conditions of the central part of the nebula, any failure of the 
law in this direction would increase the discrepancy. 
‘Popular Lectures and Addresses, I. Constitution of Matter, p. 419. 
2(Qn the Mechanical Conditions of Swarms of Meteorites, and on Theories of 
Cosmogony, Phil. Trans. Roy. Soc., 1888. 
